EP-A-2 607 636 discloses a cam follower comprising a tappet, a pin and a roller. The tappet extends along a longitudinal axis, while the pin and the roller are centered on a transverse axis. The tappet is formed with two lateral flanges, delimiting an intermediate gap between them and each comprising a cylindrical bore. The roller is positioned in the intermediate gap between both flanges and bores. The pin is fitted in the two bores, such that the roller is movable in rotation relative to the pin around its axis. The pin is caulked, in other words plastically deformed, on both opposite ends to create a mechanical connection by press-fit in the tappet bores.
When the cam follower is in service, the roller collaborates with a cam synchronized with the internal combustion engine camshaft. The rotation of the camshaft leads to a periodic displacement of a piston of the pump that rests against the tappet, to allow fuel to be delivered. The tappet is movable back and forth along the longitudinal axis in a housing, while the roller is movable in rotation around its central axis against the cam.
Classically, the tappet can be made of a polymer material. However, under high temperatures and humidity of cam follower applications, polymer materials induce problems of dimensional stability and moisture absorption. The tappet dimensions and tolerances in the housing can change, which create a risk of failure of the cam follower, and consequently a risk of failure of the engine.